The continuous generating grinding method of gear teeth has been shown to be a good finishing process also in mass production because of its high efficiency and outstanding constant precision of ground workpieces. In most cases, grinding tools were used in the past that were at the outer circumference gear-worm shaped corundum wheels--the so-called grinding worms--which rarely turned faster than at a speed of approximately 40 m/s at their circumference.
The already very high efficiency of the process may be increased even more if the circumferencial speed of the grinding tool is increased further. The problem thereby is the fact that the grinding worm is deformed by the effect of the centrifugal forces at high speed. Thereby the deformation is not only caused by the complicated stress condition, as it exists in case of a rotating disk, but also by the worm profile, which has at each angle position around the rotational axis a different axial position, whereby an uneven distribution of force is applied to the worm body circumference. Furthermore, the non-homogeneity of the specific gravity and of the modulus of elasticity of the grinding wheel body are also responsible that the grinding worm shape is deformed with increasing speed. A grinding worm rotating at high speed is therefore not only larger in its diameter than the one that is not moving, but it is generally also not round, and the once established worm profile takes on a shape that cannot be predicted in advance. This is however basically true for tools of all grinding machines, only this phenomenon is not a hindrance in cases where the active form of the grinding disk is shaped at a working speed, which means, where the deformations effected by the centrifugal force are eliminated by the dressing process to a certain degree.
Unfortunately, grinding worms are, for obvious reasons, much more difficult to be shaped than grinding disks. In the rule it is therefore necessary to conduct the dressing process at very low speed. Therefor there are a number of processes known wherein the most efficient and currently most widely known process the one with two profiling disks: each profiling disk layered with diamond grains dresses thereby one worm flank in a process, which is similar to the thread cutting process on a lathe. In another more universal method, grinding worm flanks are dressed by making contact at specific points along a line by means of a rotating dressing tool that has a layer of diamond grains at its active outer circumference. This process is performed in such a manner that line after line are placed very close to one another until the entire active flank surface is dressed. This method is however slower than the one mentioned above but it allows--within certain limits--the creation of an arbitrary topology on the worm flanks. For grinding worms shaped in this manner, there is determined in advance a specific assignment of each point of the tooth flanks to be ground to a specific point on the worm flank whereby, during subsequent grinding it must be ensured by relative motion between the tool and workpiece that the respective points are actually touched or are a common meshing point or machining point. Through this method it is possible to manufacture topologically corrected gear teeth by a continuous generating grinding process.
DE-PS 196 19 401 C1 discloses a process by which grinding worms may also be topologically dressed at top grinding speeds. However, this process places high demands on the mechanical device and on the quality of the necessary servo-drives and control systems, which leads in any case to high investment costs. In addition, dressing tools used in this process can only be used for one specific modulus pitch on the grinding worm.